1. Field of the Invention
The invention relates to a polishing pad which is useful for planarizing a semiconductor wafer or other substrate, and in particular, to a polishing pad of the type having multiple stacked layers.
2. Background of the Invention
xe2x80x9cMicroelectronic substratexe2x80x9d is intended to mean semiconductor devices or precursors thereto, including semiconductor wafers, semiconductor device layers comprising an insulator, semiconductor, barrier layer, conductor or any combination thereof.
A microelectronic substrate must be polished to provide a very smooth and planar surface that in some cases may vary from a given plane by as little as a fraction of a micron. Such polishing is usually accomplished in a chemical-mechanical polishing (CMP) operation which utilizes a chemically active slurry that is buffed against the wafer surface by a polishing pad.
A polishing pad is often a relatively thin, disk-shaped article that is mounted on a platen of a polishing machine. Some polishing pads comprise two or more layers of different materials, which are coextensively stacked and secured together by adhesive.
In the case of a stacked two layer pad, an upper layer is a polishing layer that is relatively hard and stiff to attain a high rate of material removal while maintaining a substantially planar polishing surface while removing the material during a polishing operation. The upper layer is substantially impermeable to liquid constituents borne by the slurry and to de-ionized water, which accompany a polishing pad during polishing and washing operations.
A lower layer is a sub-layer that is softer than the upper layer to cushion the upper layer. The sub-layer tends to be permeable to slurry borne liquid and de-ionized water. The sub-layer is shielded from these liquids by being coextensive with the impermeable upper layer and adhesive. However, a peripheral edge of the sub-layer is unshielded and is exposed to permeation by the liquid. By allowing liquid to penetrate the sub-layer, physical properties of the sub-layer may change, thereby changing the cushioning effect of the sub-layer to the detriment of polishing performance by the stacked polishing pad.
Further, a stacked polishing pad may be of a type that has a transparent window through which is trained an optical path for optical detection equipment to detect when a polishing endpoint is attained by a polishing operation. Allowing liquid to penetrate the sub-layer, may disturb the optical path.
The present invention is directed to a stacked polishing pad comprising a polishing layer and a sub-layer. The polishing layer is substantially liquid impermeable (or is substantially less liquid permeable than the sub-layer), while the sub-layer is liquid permeable (or at least significantly more liquid permeable relative to the polishing layer). The polishing layer that is stacked on the sub-layer provides a liquid impermeable shield for an upper surface of the sub-layer. The sub-layer is mounted against a platen of a known polishing machine, which would further shield the sub-layer. According to an embodiment of the invention, the sub-layer has an outer peripheral edge which is sealed to prevent liquid permeation into the sub-layer.
According to another embodiment of the invention, the stacked polishing pad has an opening that is delineated by an inner peripheral edge extending through the multiple layers of the polishing pad. The inner peripheral edge of the sub-layer is sealed to prevent permeation of liquid into the sub-layer.
The peripheral edge of the sub-layer may be sealed by any suitable means including a heat seal, a pressure embossed seal, and a waterproof coating.
According to another embodiment of the invention, the polishing pad is provided with one, or more than one, opening extending through the multiple layers of the polishing pad. Any of the respective inner peripheral edges of the openings may be unsealed, by having the material of the sub-layer exposed, which provides liquid absorption regions in the sub-layer adjacent to unsealed, open vias through the pad.